The present invention relates to vehicular headlamp having a reflector for controlling the luminous intensity distribution from the headlamp, wherein the reflecting surface of the reflector is composed of a plurality of reflecting regions. Each reflecting region is formed as an assembly of many small reflecting elements that take one of three fundamental shapes, i.e., a hyperbolic paraboloid, an elliptic paraboloid and a bilobate hyperboloid, and which are fixed to a reference member to form the entirety of the reflecting surface. The novel reflector that is provided in accordance with the present invention is such that the outer lens, which is positioned ahead of the reflector, need not control the luminous intensity distribution of the headlamp, while nevertheless a desired luminous intensity distribution pattern can be formed while insuring that the requirements for diffusion in the horizontal direction and formation of the central part of the pattern can be satisfied.
Conventionally, for producing a low beam in an automotive headlamp, a coiled filament is positioned near the focal point of a reflector, which is in the form of a spheroid (paraboloid of revolution) in such a way that the central axis of the filament extends parallel to the optical axis of the reflector. (This filament arrangement is generally referred to as the "C8 type"). A shade is positioned below the filament for forming a cut line (cut-off) in the luminous intensity distribution pattern.
With this arrangement, part of the light issuing from the filament is blocked by the shade, so that generally the lower half of the reflecting surface does not receive much light, and hence is not used effectively. The luminous intensity distribution of the pattern image obtained with the reflector is controlled by means of diffusing and refractive lens steps formed in the outer lens, which is positioned ahead of the reflector. As a result, there is obtained a luminous intensity distribution pattern that provides the required beam spread in the horizontal direction. Thus, conventionally, control of luminous intensity distribution by the lens steps in the outer lens has played an important role in forming a luminous intensity distribution pattern that has the appropriate cut-line characteristic of the low beam.
One of the demands on the styling of modern automobiles is to streamline the car body in order to satisfy various aerodynamic and design requirements. Under these circumstances, it has become necessary to provide a headlamp that is adaptive to the body of a so-called "slant nose" type car whose front narrows gradually. However, this has made it necessary to reduce the height of the headlamp while increasing the angle (i.e., the slant angle) the outer lens forms with the vertical axis. As a result, the height of the reflector must be decreased and, furthermore, the inclination of the outer lens made very sharp. This has led to the problem that the lens steps in the outer lens cannot properly control the luminous intensity distribution, as compared with earlier designs. This is because, with a greater inclination of the outer lens, disadvantages occur such as light attenuation by the lens and drooping of the luminous intensity distribution pattern in areas close to both the right and left ends. (This phenomenon is generally referred to as "optical drooping").
With a view to solving this problem, an increasing effort has been made to fulfill the function of controlling the luminous intensity distribution with the reflector rather than the outer lens. To this end, various techniques have been employed such as providing a reflecting surface that consists of a plurality of reflecting regions having variable focal lengths, as well as offsetting the normal axes of the respective regions. However, it has been difficult to both simultaneously provide high diffusibility in the horizontal direction and insure adequate brightness in the central area in the formation of a luminous intensity distribution pattern.